1. Field of the Invention
The present invention pertains to an apparatus and method for diagnosing a breathing disorder, and, in particular, to an apparatus that determines a dimension of a portion of a patient's airway, such as a cross-sectional area of the airway, for each of a plurality of internal loads imposed on the patient's airway and, from this information, assesses the likelihood that the patient suffers from a breathing disorder. The present invention also pertains to a method of diagnosing the likelihood that a patient suffers from a breathing disorder using such an apparatus.
2. Description of the Related Art
Obstructive sleep apnea ("OSA") is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstructed upper airway segment. Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently and repeatedly during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may translate clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonaryartery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Hypersomnolent sleep apnea patients may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Using conventional techniques, OSA cannot be readily diagnosed in a physician's office or in a hospital during a short visit. Instead, present methods for diagnosing OSA rely on polysomnography to measure the patient's apnea/hypopnea index ("AHI"), which takes place over a period of several hours while the patient is asleep, typically during an overnight sleep monitoring session. This conventional diagnostic technique commonly takes place in a sleep laboratory, which is in a hospital or a clinic. Portable polysomnography devices exist that enable the sleep monitoring session to take place at the patient's home. However, home monitoring requires that the patient place the monitoring system and sensors on himself or herself and operate the polysomnography monitoring device, which may result in erroneous or inefficient placement of the sensors and/or improper use of the monitor. A caregiver may assist the patient at home in placing the sensors and operating the monitoring system. However, this is costly and time consuming.
It can be appreciated that the conventional overnight procedure for diagnosing OSA, whether in a sleep lab or at home, is time consuming for both the patient and the technician monitoring the patient. This diagnostic technique is also generally inconvenient and may be unsettling to the patient because it typically requires that the patient stay in the hospital or the clinical setting overnight and that the patient wear a myriad of sensors while trying to sleep. The likelihood that the monitoring session will be unsettling is especially true for children and patient's with an elevated level of apprehension concerning medical facilities, such as patient's with infirm mental abilities.
Conventional OSA diagnostic procedures also requires a significant amount of processing of complex physiological data by a trained technician, which, again, is time-consuming and costly. Thus, conventional diagnostic procedures, because of their overly burdensome and perhaps onerous techniques, as well as exorbitant expense, are not suitable as a prescreening tool to determine if there is even a likelihood that the patient may suffer from OSA. Rather, conventional diagnostic techniques are best used if it is already determined that there is a likelihood that the patient suffers from OSA. In which case, the conventional techniques can be more appropriately targeted to functions such as determining an appropriate therapy to treat the patient. A practical and reliable prescreening technique would identify patients who are not likely to suffer from OSA so that they can avoid the relatively time consuming and burdensome overnight diagnostic session and also identify those patients who are likely suffers from OSA so that additional diagnosis (if necessary) and treatment can be obtained.
Indications for sleep apnea are generally a patient's complaint or the complaints of a spouse or a sleep partner of daytime somnolence and/or frequent awakening episodes while sleeping or trying to sleep. These indicators, however, are highly subjective and may be attributable to other factors. In addition, some OSA sufferers, including children and patients afflicted with Down's Syndrome, have difficulty clearly communicating the nature of their problem with sleep interruption. Thus, these indicators, whether elucidated from the patient via a written questionnaire or orally, are not entirely reliable as a prescreening indication of OSA. Also, physical indicators, such as increased lung residual volume or subsequent cardiovascular complications, are also generally not strong indicators of OSA.